The present disclosure relates to solar cells, and more specifically, to multi-junction solar cells.
Multi-junction solar cells can include multiple solar cells made of different semiconductor materials and comprise multiple p-n junctions. Using multiple semiconducting materials can allow a multi-junction solar cell to absorb a broader range of wavelengths of light. For example, a first solar cell can have a bandgap energy that requires at least the absorption of a blue photon (450-495 nm wavelength) for an electron to have the bandgap energy to move from the valence band to the conduction band. As a result, light with wavelengths greater than blue photons may pass through the first solar cell. However, a second solar cell having a bandgap energy that only requires the absorption of a red photon (620-750 nm wavelength) for an electron to have the bandgap energy to move from the valence band to the conduction can be placed at a back surface of the first solar cell. Light that passes through the first solar cell may then be absorbed by the second solar cell, potentially improving the sunlight to electrical energy conversion efficiency.